Analog input configuration

With PiCtory, you can configure your RevPi AIO. In this chapter, we will describe the Value Editor settings for analogue inputs in greater detail.

Requirements:

A web browser is installed on your PC (e.g. Chrome or Firefox).

RevPi Core is to be found in your network.

Let’s go!

Your AIO has 4 analog inputs. The inputs can be set either as a voltage input or as a current input. You can connect up sensors like, for example, proximity sensors or level sensors with analog outputs (generally 4-20 mA or 0-10 V).

So that a configuration can function, it is important that your devices are connected to the right input pins.

Input 1

PIN

Use

24

– negative input for current or voltage measurement channel 1

26

* from here to pin 28, a wire jumper has to be fitted for measuring current

28

+ positive input for current or voltage measurement channel 1

Input 2

PIN

Use

23

– negative input for current or voltage measurement channel 2

25

* from here to pin 27, a wire jumper has to be fitted for measuring current

27

+ positive input for current or voltage measurement channel 2

Input 3

PIN

Use

17

– negative input for current or voltage measurement channel 3

19

* from here to pin 21, a wire jumper has to be fitted for measuring current

21

+ positive input for current or voltage measurement channel 3

Input 4

PIN

Use

11

– negative input for current or voltage measurement channel 4

13

* from here to pin 15, a wire jumper has to be fitted for measuring current

15

+ positive input for current or voltage measurement channel 4

Open your web browser.

Enter the IP address of your RevPi Core in the address bar of your web browser.

The login window appears.

Log in with the username “admin”.

Enter the password. You can find it on the sticker on the side of your RevPi Core.

Click on “Login”

You will now see the current device status of your RevPi Core.

Click the “Apps” tab.

Click the start button behind the entry “PiCtory”.

PiCtory opens.

Open the folder “I/O Devices” in the device catalog.

Select AIO.

Drag and drop the AIO into the empty slot on the Configuration Board.

Determine the basic settings for your adapter in the “Device Data” section. This is optional. The settings however can be useful when using many devices and you would like to process the data in another programme at a later point in time.

You can configure your inputs in Value Editor. The detailed settings are to be found in the following table.

Description

Value

Comment

Input1Range,
Input2Range,
Input3Range,
Input4Range

-10- 10 V

0 – 10 V

0 – 5 V

-5 – 5 V

0 – 20 mA

0 – 24 mA

4 – 20 mA

-25 – 25 mA

Set here the input range for voltage or current measurement. The measurement process (current or voltage) as well as the range should match the output of the connected sensor. Typical for industrial sensors is 0-10 V or 4-20 mA.

ADC_DataRate

5 Hz

10 Hz

20 Hz

40 Hz

80 Hz

160 Hz

320 Hz

640 Hz

Set the frequency that is then used as the data rate for the analog converter.
The rate by which the value is updated in the process image is about 1/5 of this data rate.
The frequency applies to all 4 inputs.

Skalierung Eingang 1-4:
Input1Multiplier
Input1Divisor
Input1Offset

16 Bit signed Multiplier

16 Bit unsigned Divisor

16 Bit signed Offset

Here you can determine a scale for every input channel. It is determined by the three configuration values and calculated according to the following formula from the original value (available as mV or µA):

Y = Multiplier/Divisor*X + Offset

Please remember that you can always only measure current or voltage on a channel. When measuring current, a shunt is performed between the inputs for measuring the power via a jumper, which you have to fit yourself. The resetting of the ranges in PiCtory initially changes little in the measurement electronics but is only used for conversion in mV or µA as well as the monitoring of limit values. Only the input sensitivity of the measuring sensitivity for the 0-5 V range is increased, whereby a two-fold accuracy (max deviation is 5 mV in this range) is achieved.

The scaling can be used for the conversion into other units or for a subsequent calibration of a sensor. When calculating in an AIO Modul, a 32-bit Integer Arithmetic is used. The results are then stored again as 16-bit values in the process image. Should the result Y exceed the limits of a 16-bit signed value, then the error is recognised and the value limited. The initial values always lie in the unit mV or µA respectively.

Example:

A proximity sensor emits 0 to 10 volts in the range between 30 and 300 millimetres. To have the gap shown in mm you have to select the parameter as follows:

Multiplier = 270, Divisor = 10000, Offset = 30

Should the sensor work instead with 4-20 mA, the values have to be set as follows:

Multiplier = 270, Divisor = 16000, Offset = -38

About the ADC_DataRate:

The module uses a Delta Sigma Converter – model ADS 1248. The converter has an adjustable data rate that is closely linked to the frequency response of the digital filter to be found in such a converter. Precise diagrams for frequency responses attained for each setting are to be found in the ADS 1248 data sheet on pages 31 and 32. Important for your measurements is here that low-frequency interfering signals, like for example a 50 Hz humming, can only be effectively supressed at settings from 5 to 20 Hz. The greatest measurement accuracy comes therefore with these settings. On the other hand, the updating rate of the data values in the process image is thus reduced. The links are as follows:

Please note that the table values for the 320 Hz and 640 Hz settings only show the maximum values. The actual updating rate can, in this range, be significantly lower due to the load on the PiBridge. The load is dependent on your configuration and can, for these ADC_DataRates, therefore only be established experimentally on your system and with your configuration. Generally, these settings are not to be recommended.

Click on „File>Save“. You thus save your file.

Click on „Tools>Reset Driver“. You thus activate the changes for the adapter.

Should an error occur, you will receive error messages in the input values of the process image with the names InputStatus_1-4. The values have the following meanings:

Bit position

Status message

Bit 0 (LSB)

0 = value is higher than the lower limit for the configured range

1 = value is at least 20 mV or 20 µA respectively lower than the lower limit of the configured range

Bit 1

0 = value is lower than the upper limit of the configured range

1 = value is at least 20 mV or 20 µA respectively higher than the upper limit of the configured range.

In the InputValue_1-4 fields, you can now see the actual value of the input. If you use an input as the voltage input, the value is shown in mV. If you use the input as a current input, the value is shown in µA.

In the InputValue_1-4 fields, you can determine the symbolic names for the 4 analog input values. Under this name you can then, using PiTest, an own-programme or an application software, read measurement values from the connected sensors from the process image. The values are shown there for the voltage ranges in mV and for the current ranges in µA should you have left the scaling at 1.

Would you like to continue to use the settings in logiCAD3, Python or C?

Then click on “File>Export”.

A window will now open. Here you can determine the format of the file and give the file a name.

You can choose between 2 formats:

Export 01 creates a file suitable for use in logiCAD3.
Export 02 creates an Offset List that you can use as basic information for an own C or Python programme.

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